EL is phospholipase belonging to triglyceride lipase (hereinafter, referred to TGL) family (Non-patent document 1). Human EL consists of 500 amino acid residues (NCBI Accession No. NP_006024.1) and mouse EL also consists of 500 amino acid residues. Lipoprotein lipase (hereinafter, referred to LPL) and hepatic lipase (hereinafter, referred to HL) are included in TGL family.
The analysis of EL knockout mice and EL transgenic mice revealed the involvement of EL in HDL cholesterol (hereinafter, referred to HDL-c) metabolism due to its strong phospholipase activity for HDL, and EL is noted as a determinant of HDL levels (Non-Patent Document 2). The negative correlation between coronary artery disease (hereinafter, referred to CAD) and plasma HDL-c levels has been known for a long time. HDL-c has been believed to show anti-atherogenic effect via anti-oxidant, anti-inflammatory and reverse cholesterol transport action and low HDL-c cholesteremia has been recognized as one of the risk factors for CAD. Therefore, EL inhibitor can be a therapeutic agent against CAD, and the increase in HDL-c levels and the decrease of atherosclerotic lesion area have actually been reported in the animal model of disease using EL-knockout mice (Non-Patent Document 3).
These findings exhibit utility of a specific inhibitor for EL as a therapeutic agent against lipid metabolism disorder and atherosclerosis.
In evaluation of drug efficacy of EL inhibitor, it is important to grasp the degree of inhibition of EL in blood by administered drug in order to understand the potency of drug efficacy. However, because other enzymes having lipase activity similar to EL exist in blood, the finding of assay method which can detect EL activity specifically is a problem to be solved for selecting a promising inhibitor.
The lipase having higher activity than EL exists in blood under the general assay condition well known (Non-Patent Document 4). Thereby, as EL activity can not be measured accurately, it is difficult to accurately determine inhibition rate of administered EL inhibitor in blood. When blood is collected to measure EL activity in non-clinical study, it is necessary to administer a large amount of heparin intravenously in order to release and collect EL from blood vessel wall, but intravenous injection of a large amount of heparin to a subject is not allowed in clinical trial. Therefore, the marker as an indicator of EL activity is essential for clinical trial, whereas there has never been any report about the presence of maker for EL activity.
Non-Patent Document 1: Nature Genetics., 1999, vol. 21 (4), p. 424-428
Non-Patent Document 2: TCM., 2004, vol. 14 (5), p. 202-206
Non-Patent Document 3: The Journal of Biological Chemistry., 2004, vol. 279 (43), p. 45085-45092
Non-Patent Document 4: The Journal of Clinical Investigation, 2003, vol. 111 (3), p. 347-355